Grinder for rock drills



1952 N. H. B. KRISTENSON 2,619,779

GRINDER FOR ROCK DRILLS Filed Feb. 28, 1950 2 SHEETSSHEET 1 Fly-1. 49 36 25 N. H. B. KRISTENSON GRINDER FOR ROCK DRILLS Dec. 2, 1952 2' SHEETSSHEET 2 Filed Feb. 28, 1950 M f v "w a M 6 m W M. a r m Patented Dec. 2, 1952 UNITED STATES, PATENT OFFICE Nils Henry l iorie Kristenson, Stockholm, Sweden, assignor to Akti'ebolaget'Kristenson & Griihs, Stockhoim Sweden, a corporation of Sweden Application February 28, 1950, Serial No. 146,667

In Sweden March 11, 1949 19 Claims.

The presentinventionrelates to drillgrinders, and itrelates more particularly to. grindersfor rock drills, especially suchv rock drills. as are provided with a cutting edge of hard metal.

It is an object of, the invention to provide, a grinder, particularlyfor rock drills, bym'eans of which ,an entirely uniform grindingor sharpening of. ,differentdrill's is obtained independently of the wearing down of the grinding disk used.

With the above and other objects. inview. a grinder has been provided according tothe invention, comprising a rapidly rotating, preferably. cup-shaped grinding, disk, which. isswingable back and forth about an axis,..which forms an angle with the saidaxis of, rotationandjis substantially parallel with the longitudinalaxis of the drill in its grinding position. This arrangement results in that for each re-sharpeningof thedrill layers of materiahof uniform thickness are ground away from the sides of the cutting edge, whereby unnecessary grinding away of material is avoidedandthe lifeetime ,Ofthe drill is considerably increased.

In a particularly suitable embodiment, of the grinder according to the invention the swinging axis of the grinding disk is horizontal and positioned at a higherelevationthan the drill in its grinding position, so that the centerof gravity of the swingable grinding unit will become posi, tioned below the swinging axis, thegrinding unit thus forming a pendulum which may be readily kept in oscillations by hand during the grinding operation.

re a h nd jar an dfflor anip ing h f r in itionhin th ram a diQ e ng th gr n un t ar the .d iltrreistably on e w n i a s. o ih un t; Sa feeding movement may be effected either by hand or automatically, for example in dependenceof the pendulum oscillations of the grinding unit.

In a grinder arranged according to the invention the size ofcutting edge angle ofthe ground or sharpened drill will be dependent on the angle between the axis of rotation of the grinding disk and the swinging axis of the grinding'unit, whereas the curvature of theoutting edge of the drill will depend on the distance between the swinging axis and the longitudinal axis of the drill. The grinder is preferably arranged so that the said angle and distance can :be variedyfor obtaining the cutting edge angle'and curvature being most suitablefor each particular drilling work.- Other features and advantages of the grinder according to the invention willbecome apparent from the following detailed description of a suitable embodiment with reference to the accompanying drawings.

In the drawings:

Fig. 1 is a side view of the grinder,

,Fig. 2 is a top view thereof,

Fig. 3 is an end View seen from. the left in Figs. land2, a

Fig. 4 is apartial section on a largerfscale taken on the line 44 in Fig. 2, and

Fig. 5 is a cross section on the line 5-5i'n Fig. 4. X- 7 The grinder illustrated on the drawings comprises a frame Ii! in theshape ofan upwardly open box, one end-wall of which is extended .upwardly to form a bearing bracketv I I, in which "is horizontally secured a bearing pin48 having the axis I2-.I2. Swingably journaled oh the horizontal bearing pin 48 is the hub I3 .of an arm, in which is provided a circularlyv curvedslot I5. Secured on the arm I4 by means of two bolts l6, which extend through the slot. I5, is a plate 'II, exchangeable washers I8 being preferably inserted between the arm and theplate... Provided in the plate are two parallel slots I9,'which form a substantially rightangle with a .line extending through the holes providedin theplate forthe fastening bolts It. By means of two bolts 20, which extend through the slots It, there. is secured to the plate on the side thereof turned away from the arm M an electricgrinding motor 2| provided on the end of the motor shaft with a cup-shaped grinding disk '22. Secured to the plate I! by means of screws'23 and "an extension lug 24 is a protective housing 25jfor the grinding disk, said protective housing coveringthe circumference of the disk and the greater portion of the active end-surface thereof, as is clearly shown in Fig. 2.

As will be clear from Fig. 1, the arm is curved in such a manner that the center line 26 26 of the grinding motor shaft will take up an inclined position with respect tothe swinging axis |2-I2 of the arm I4. The swingingaxis I2-I2 and the axis of rotation 2626 may lie in the same plane so as to intersect one another, butithe swinging axis may also, as shownin the drawings, cross the axis of rotation withoutintersecting the same. y .1

For the purpose of, varying the size'of the cutting edge angle, the inclination betwe'eri th e' axis of rotation 25-26 and the swinging axis I2' l2 can be varied by displacing thebolt's I 6 in either direction along the slot I5. Furthermorefth'e grinding disklcan be displaced in thedirectidiiof the axis 25-25 with respect to the protective housing 25 by displacing the bolts 29, after loosening them, in either direction along the straight slots i9. Said latter setting possibility has been provided to render possible compensation for the wearing down of the grinding disk.

The grinding unit 2 I, 22 suspended in the above described manner can evidently oscillate about the swinging axis |2-|2. The grinding unit 2!, 22 may then be kept in oscillations by hand, either by means of a handle 21 clamped in position to the arm l4 under the head of one of the fastening bolts 16, or by means of an arm 29 extending radially down from the hub I3 on the outside of the bearing bracket l l and provided with a hand ball 28.

Said hand ball 28 is fastened on the outer end of a transversely extending pin 33, which is displaceable axially against friction in a hole provided in the arm 29, so that the pin can be inserted with its inner end into a hole 3! in the frame 10 for the purpose of locking the swinging arm 29 and consequently also the grinding unit 2|, 22 in a definite position with respect to the frame. When the swinging arm 29 is locked by means of the pin 30, the grinding unit can evidently be used as an ordinary grinding machine. To enable access to the circumferential surface of the grinding disk the protective housing 25 may be provided with a detachable section 32 and with a support 33 for the work piece to be ground.

For clamping the drill 35 in the frame It during the operation of sharpening its cutting edge there is provided on the frame at the side thereof being opposite to the bearing bracket ll a holder consisting of a bracket 36, which by means of a bolt 3! can be clamped in a suitable position on the frame and which is provided with a substantially vertical or steeply sloping surface 38, to which the lower clamping jaw 39 for the drill can be secured by means of two bolts 49. The upper clamping jaw 4| can be clamped against the lower jaw or against the drill respectively in ordinary manner by means of a screw nut 43. provided with a handle 42. For reading the setting position of the bracket 36' inthe lateral direction there is provided on the bracket a scale 44, which co-operates with a zero mark 45 on the frame, whereas to enable reading of the setting position of the lower clamping jaw 39 in a vertical direction, the lower jaw is provided with a scale 46 which co-operates with a zero mark 41 on the bracket.

The possibility of moving the bracket 35 ina lateral direction involves a possibility of compensating for variations in the thickness of the drill shank. To prevent the cutting edge of the drill from becoming unsymmetrical with respec to the hard metal plate provided in the head of the drill the center line of the drill must always take up substantially the same position, independently of the thickness of the drill head.

The substantially vertical displacement of the drill head renders possible a setting of the machine for different cutting edge radii, the raising of the drill head resulting in a reduction or shortening of the radius of the cutting edge, and vice versa.

The mechanism for feeding the grinding unit towards the drill during the grinding operation is shown in Figures 4 and 5. According to said figures, the hub [3 of the pendulum arm I4 is turnably journalled through the intermediary of two bearing sleeves 49 pressedinto the hub on a bearing pin 48, which is clamped in horizontal position in the bearing bracket ll. Inserted in an inner axial bore 50 in the bearing pin 48 is a helical spring i, which presses against a disk 52, which is inserted in the mouth of the bearing bore of the hub, and holds said disk 52 pressed against a collar 54 on the end of a spindle 55 through the intermediary of bearing balls 53. Said spindle extends through a guide hole 56 out through an outer axial bore 51 in the bearing pin 48 and enters with its threaded outer end into a threaded center hole 58 in a feeding hand wheel 59. The feeding Wheel 59, which is turnably journalled by means of a pinshaped extension 65 of its hub in the outer axial bore 51, is held pressed against the annular end surface of the bearing pin 48 by the tensionof the spring 5| through the intermediary of the collar 54 and the screw spindle 55. If the hand wheel 59 is turned with respect to the spindle 55, the spindle will be displaced together with the collar 54, the hub l3 and the pendulum arm 14 in either direction along the axis l2-l2.

To prevent the spindle 55 from following the hand wheel 59 in its turning movement, there is secured to the spindle a collar 6| through which and the spindle there is taken up a diametrically extending bore, into which is pressed a short pin 62 which retains the collar in position on the spindle. Helical springs 63 engage with their inner ends the ends of the pin 62 and press with their outer ends friction bodies 64, which are inserted into the mouths of the bores, against the inside of the axial bore 51 in the bearing pin 48, so that a greater force is required for turning the spindle 55 in the pin 48 than forturning the wheel 59 on the spindle 55.

For the purpose of securing an automatic feeding movement of the grinding unit there is fastened on the inner end of the spindle 55 a collar 54 provided on its circumference, as shown in Figures 4 and 5, with ratchet teeth 65 which cooperate with a spring operated ball 66 positioned in a radial bore in a lid 61 screwed onto the end of the hub 13. The toothed collar 54 forms together with the spring actuated ball 66 a ratchet coupling between the spindle and the hub, so that the spindle is turned step by step when the hub is turned back and forth, the spindle then slowly displacing the hub and thus the entire grinding unit in the direction of its swinging axis. To prevent the hand wheel 59 from following the spindle 55 during the rotation of the latter it is suitable to insert in a bore in the extension 60 of the hand wheel hub a spring actuated friction body 68 which presses against the cylinder wall of the bore 51 in the bearing pin 48.

The grinder described above operates in the following manner.

After the grinding unit 2|, 22 has been pulled back to the position shown in Fig. 4, the drill 35 to be sharpened is clamped between the clamping jaws 39 and 4| with the head of the drill in touch with the grinding disk 22. The grinding disk is then retracted from direct contactwiththe drill by turning back the hand wheel 59 a fraction of revolution, Whereafter the motor is started and the grinding unit by means of the handle 2'! or 28 is caused to swing back and forth about the axis |2-l2. For each fulloscillation of the grinding unit the feed spindle 55isauto matically turned through one or more tooth pitches, and the grinding unit is thereby slowly fed towards thedrill. When one side of the'cutting edge has been ground ready-the clamping jaws for the'drill are loosened, the drill is turned through 180 about its axis and clamped to the frame in its turned around position, whereupon the other side of the cutting edge is ground in the same manner as the first one.

During the swinging movement of the grinding unit 2|, 22 back and forth about the stationary axis I2l2 the operating zone of the grinding disk 22 evidently will describe a conical surface, so that the opposed side of the cutting edge will obtain a corresponding conical shape. The cutting edge is formed along the line of intersection between the two conical surfaces. For reasons of the symmetry, the cutting edge can also be said to be defined by the line of intersection between one conical surface and a plane which is perpendicular to the axis of the cone. The radius of curvature of the cutting edge will thus become the larger the greater is the distance between the said plane and the apex of the cone, i. e. it becomes dependent on the distance of the drill from the;swinging axis |2i2 of the grinding unit. Since said distance remains constant independently of the wearing down of the grinding disk, the cutting edge and the cutting edge angle will always get the same shape and size respectively. This involves that during each re-sharpening of a drill a surface layer of even thickness is removed, so that every unnecessary removal of material from the end of the drill is avoided. Each drill can thus be re-sharpened a greater number of times than would otherwise be possibie, resulting in an improved drill economy.

When grinding or sharpening drills having hard metal cutting edges the grinding disk will be Worn down very rapidly, so that in continuous use of the grinder one grinding disk may become completely worn down in one day. Said wearing-down of the grinding disk has no influence on the size of the cutting edge angle or on the shape of the cutting edge proper but results in that the working surface of the grinding disk is retracted more and more into the protective housing 25 and becomes more difficult of access. It may therefore be suitable to compensate for the wearing-down of the disk by now and then moving forward the grindin unit 2!, 22 in the direction of the grinding disk spindle. This can be effected by moving the fastening bolts 26 for the grinding motor to a new position in the slots l9 provided in the supporting plate for the motor.

In the embodiment of the grinder shown in the drawings the grinding unit is so arranged that the axis of the grinding disk 22 is displaced somewhat in the lateral direction from a vertical plane through the swinging axis I2--i2, so that the drill will engage the grinding disk approximately on a horizontal diameter of the disk, which generally is preferable. Such a desired unsymmetrical positioning of the grinding unit may be obtained by loading of the pendulum arm H! with suitable weights. It is, however, better to use a compensating spring for this purpose. In the embodiment shown the feed spring 5| has been arranged to act at the same time as a compensation spring, in that the spring engages with one end a pin 59 secured in the stationary bearing pin 48, and with its other end a pin 10 which is secured in the disk 52 inserted into the mouth of the bore of the hub. Through a suitable positioning of the pins 69 and m the feed spring 5| can be given an initial torsional tension, which keeps the grinding unit in the desired starting position.

The invention is, of course, not limited to the embodiments shown on the drawings but modifications of different kinds are conceivable within the scope of the invention.

I claim:

1. In a grinder for rock drills, a frame, a grinding unit comprising a grinding disk and means for rotating said grinding disk, a carrier supporting said grinding unit, said carrier being swingably mounted on said frame, the swinging axislof said carrier forming an acute angle with the rotating axis of said disk, the latter having a transverse surface adapted to operate as the working surface, means for releasably securing said drill to said frame, the longitudinal axis of said drill in operative position being substantially parallel with and spaced from the swing axis of said carrier. j

2. The grinder, as set forth in claim 1, which includes means for relative feeding between the drill and the grinding disk substantially in the direction of the swinging axis of the carrier.

3. The grinder, as set forth in claim 1', in which the swinging axis of said carrier is disposed substantially horizontally.

4. The grinder, as set forth in claim 1, in which the swinging axis of said carrier is disposed at a higher level than the longitudinal axis of said drill in its operative position.

5. The grinder, as set forth in claim 1, in which the axis of rotation of the grinding disk crosses the swinging axis of said carrier without intersection.

6. The grinder, as set forth in claim 1, which includes means for varying the angle between the axis of rotation of the grinding disk and the swinging axis of the carrier, in order to vary the size of the cutting edge angle of the drill.

7. The grinder, as set forth in claim 1, which includes means for varying the distance between the swinging axis of the carrier and the longitudinal axis of the drill in its operative position, in order to vary the curvature of the cutting edge proper.

8. The grinder, as set forth in claim 1, which includes means for moving the grinding disk along its own axis of rotation, thereby compensating for the wearing down of the disk.

9. The grinder, as set forth in claim 1, in which said securing means for the drill comprise a clamping member retaining the drill in position during the grinding operation, and additional means for feeding the grinding disk towards the drill in the direction of the swinging axis of the carrier.

10. The grinder, as set forth in claim 1, in which said carrier supporting said grinding unit comprises a pendulum arm, the latter being swingable about the said swinging axis.

11. The grinder, as set forth in claim 10, which includes a feed screw for said pendulum arm and in which the latter is displaceable in the direction of the swinging axis under the action of said feed screw.

12. The grinder, as set forth in claim 11, which includes a stepping mechanism to automatically turn the feed screw in the feed direction under the action of the pendulum arm during the swinging movement of the latter.

13. The grinder, as set forth in claim 12, which includes a stationary bearing pin suspending said pendulum arm, said bearing pin having a center bore receiving said feed screw, and which includes further a feeding hand wheel, having a threaded center bore and cooperating with said feed screw.

gamma 14.- The grinder, asset forth in claim 13', in which said feed screw is disposed coaxially with said bearing pin and is rotatably mounted in a portion of said pendulum arm, said portion extending beyond the end of said bearing pin.

15. The grinder, as set forth in claim 14, in which said feed screw carries a wheel having ratchet teeth and which includes a spring actuated ball disposed in a bore of said pendulum arm, thereby stepping forwardly thewheel in one direction upon swinging back and forth the said pendulum arm.

16; The grinder, as set forth in claim 15, in which said screw spindle has secured thereto a friction device pressing against the inner wall of said bearing pin in order to prevent the turning of the spindle when turning the hand wheel.

1'7. The grinder, as set forth in claim 16, in which said hand wheel has a fric'tiondevice'disposed in a bore of said wheel and pressing against theinner wall of the bearing pin.

18.- The grinder, as set forth. in claim 1, in which said means for releasably securing said drill to said frame comprises a bracket supported by said frame, said bracket having a steeply sloping surface receiving the clamping device and 15 Number Name Date- 431,422 W'atrou's July 1, 1890 965,952 Schmaltz' Aug. 2', 1910 1,698,909 Currier Jan. 15', 1929 2,017,532 Elt'er et a1 Oct; 15, 1935 20 2,133,386 Galloway Oct. 18, I938 2,151,204 Hartman Mar. 21, 1939 2,392,478 Holman Jan. 8, 1946 FOREIGN PATENTS 25' Number Country Date 621,087 Great Britain Apr. 4,. 1949 81 said bracket having a graduation in order to permit of reading ofv the setting position.

19. The grinder; as set forth in claim 18,. in which the bracket is displaceable along the frame in a horizontal direction and perpendicularly to the direction of the drill and in which said bracket hasa' graduation for reading the setting position;

NILS HENRY BoRJE KRI'sTENs'on'.

REFERENCES CITED The following references are of record iii the file of this patent:

UNITED STATES PATENTS 

